The “Hollow Mask” illusion

When John Robert Colombo asked if I was aware of this illusion, I replied that I was. I used to make plaster casts of sculpted heads and noticed it then.

What came as a surprise was the ecclesiastical application that JRC had experienced. From his email message to me:

For a number of years we visited […] Beloeil where we would walk into the very large and old church, Eglise Saint-Matthieu. My eye would be attracted to the larger-than-life statue of the Virgin Mary because of its notable feature, the one above and beyond its stark white marble surface. The statue had what I took to be an “all-seeing eye.” It certainly “followed me around.” But its gaze was not focused on me but beyond me. Up close I realized the effect was of an “all-seeing face,” created by rendering the head (surrounded by billowing cloth, as I recall) not in relief but in reverse of relief. (There is a term here that is eluding me.) Rather than the nose sticking out, the nose is stuck in, and the other features follow suit. The effect, when noted, is somewhat eerie. Have you encountered this technique before? If so, what is it called?